Drug Heating Cycle Limiter For Injection Device

ABSTRACT

An injection assembly includes a dispensing chamber housing, a temperature control device, a thermal sensor, a switch, and a controller. The dispensing chamber housing has an inner surface and an outer surface. The inner surface partially defines a dispensing chamber for receiving a quantity of a substance. The temperature control device at least partially surrounds the dispensing chamber housing and alters a temperature of a substance in the dispensing chamber. The thermal sensor is located near the temperature control device and reads a temperature near the temperature control device. The switch is coupled to the temperature control device. The controller controls the temperature control device and the switch such that a first voltage is applied to the temperature control device until the temperature control device reaches a desired temperature, and a second voltage is applied to the temperature control device thereafter to maintain the temperature control device at the desired temperature.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/581,629 filed Oct. 16, 2006, U.S. patent application Ser.No. 11/581,630 filed Oct. 16, 2006, U.S. patent application Ser. No.11/581,591 filed Oct. 16, 2006, and is related to U.S. patentapplication Ser. No. 11/435,906 filed May 17, 2006.

BACKGROUND OF THE INVENTION

The present invention relates to a single-use medical device and moreparticularly to a two-piece ophthalmic injection device with adisposable tip end containing a temperature control device andtemperature sensor assembly.

Several diseases and conditions of the posterior segment of the eyethreaten vision. Age related macular degeneration (ARMD), choroidalneovascularization (CNV), retinopathies (e.g., diabetic retinopathy,vitreoretinopathy), retinitis (e.g., cytomegalovirus (CMV) retinitis),uveitis, macular edema, glaucoma, and neuropathies are several examples.

These, and other diseases, can be treated by injecting a drug into theeye. Such injections are typically done manually using a conventionalsyringe and needle. FIG. 1 is a perspective view of a prior art syringeused to inject drugs into the eye. In FIG. 1, the syringe includes aneedle 105, a luer hub 110, a chamber 115, a plunger 120, a plungershaft 125, and a thumb rest 130. As is commonly known, the drug to beinjected is located in chamber 115. Pushing on the thumb rest 130 causesthe plunger 120 to expel the drug through needle 105.

In using such a syringe, the surgeon is required to pierce the eyetissue with the needle, hold the syringe steady, and actuate the syringeplunger (with or without the help of a nurse) to inject the fluid intothe eye. The volume injected is typically not controlled in an accuratemanner because reading the vernier is subject to parallax error. Fluidflow rates are uncontrolled and tissue damage may occur due to an“unsteady” injection. Reflux of the drug may also occur when the needleis removed from the eye.

An effort has been made to control the delivery of small amounts ofliquids. A commercially available fluid dispenser is the ULTRA™ positivedisplacement dispenser available from EFD Inc. of Providence, R.I. TheULTRA dispenser is typically used in the dispensing of small volumes ofindustrial adhesives. It utilizes a conventional syringe and a customdispensing tip. The syringe plunger is actuated using an electricalstepper motor and an actuating fluid. Parker Hannifin Corporation ofCleveland, Ohio distributes a small volume liquid dispenser for drugdiscovery applications made by Aurora Instruments LLC of San Diego,Calif. The Parker/Aurora dispenser utilizes a piezo-electric dispensingmechanism. Ypsomed, Inc. of Switzerland produces a line of injectionpens and automated injectors primarily for the self-injection of insulinor hormones by a patient. This product line includes simple disposablepens and electronically-controlled motorized injectors.

U.S. Pat. No. 6,290,690 discloses an ophthalmic system for injecting aviscous fluid (e.g. silicone oil) into the eye while simultaneouslyaspirating a second viscous fluid (e.g. perflourocarbon liquid) from theeye in a fluid/fluid exchange during surgery to repair a retinaldetachment or tear. The system includes a conventional syringe with aplunger. One end of the syringe is fluidly coupled to a source ofpneumatic pressure that provides a constant pneumatic pressure toactuate the plunger. The other end of the syringe is fluidly coupled toan infusion cannula via tubing to deliver the viscous fluid to beinjected.

It would be desirable to have a portable hand piece for injecting a druginto the eye. Such a hand piece can include a limited reuse assemblyattachable to and removable from a disposable tip segment. Thedisposable tip segment contains the drug, a needle for administering thedrug, and a temperature control device, such as a heater, for alteringthe temperature of the drug. Typically, the drug is suspended in acompound that is heated. In order to maintain the integrity of the drug,it is desirable to limit the number of times it is heated. Therefore, itwould be desirable to implement a drug delivery hand piece with such aheating limitation.

SUMMARY OF THE INVENTION

In one embodiment consistent with the principles of the presentinvention, the present invention is a dispensing assembly including adispensing chamber housing, a temperature control device, a thermalsensor, and a controller. The dispensing chamber housing has an innersurface and an outer surface. The inner surface partially defines adispensing chamber for receiving a quantity of a substance. Thetemperature control device at least partially surrounds the dispensingchamber housing and alters a temperature of a substance in thedispensing chamber. The thermal sensor is located near the temperaturecontrol device and reads a temperature near the temperature controldevice. The controller controls the temperature control device such thatthe substance in the dispensing chamber is not exposed to temperaturestress.

In another embodiment consistent with the principles of the presentinvention, the present invention is an injection assembly including adispensing chamber housing, a temperature control device, a thermalsensor, a switch, and a controller. The dispensing chamber housing hasan inner surface and an outer surface. The inner surface partiallydefines a dispensing chamber for receiving a quantity of a substance.The temperature control device at least partially surrounds thedispensing chamber housing and alters a temperature of a substance inthe dispensing chamber. The thermal sensor is located near thetemperature control device and reads a temperature near the temperaturecontrol device. The switch is coupled to the temperature control device.The controller controls the temperature control device. The controllercontrols the switch such that a first voltage is applied to thetemperature control device until the temperature control device reachesa desired temperature, and a second voltage is applied to thetemperature control device thereafter to maintain the temperaturecontrol device at the desired temperature.

In another embodiment consistent with the principles of the presentinvention, the present invention is a method of operating a dispensingassembly including checking a count of a number of times a temperaturecontrol device has been activated; if the count does not exceed a presetnumber, incrementing a counter; applying a first voltage across atemperature control device to bring the temperature control device to adesired temperature; after the temperature control device reaches thedesired temperature, applying a second voltage across the temperaturecontrol device to maintain the temperature control device at the desiredtemperature; then starting a timer to count the amount of time that thetemperature control device is activated; and if the amount of time thatthe temperature control device is activated exceeds a preset amount oftime, the temperature control device is turned off.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are intended to provide further explanation of the invention asclaimed. The following description, as well as the practice of theinvention, set forth and suggest additional advantages and purposes ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, which are incorporated in and constitute apart of this specification, illustrate several embodiments of theinvention and together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a perspective view of a prior art syringe.

FIG. 2 is a view of an ophthalmic medical device including a disposabletip segment and a limited reuse assembly according to the principles ofthe present invention.

FIG. 3 is an embodiment of a limited reuse assembly according to theprinciples of the present invention.

FIG. 4 is a cross section view of a disposable tip segment and a limitedreuse assembly according to the principles of the present invention.

FIG. 5 is a cross section view of a disposable tip segment according tothe principles of the present invention.

FIG. 6 is a block diagram of an implementation of a drug heating cyclelimiter according to the principles of the present invention.

FIG. 7 is a block diagram of an implementation of a drug heating cyclelimiter according to the principles of the present invention.

FIG. 8 is a graph of one operation of a drug heating cycle limiteraccording to the principles of the present invention

FIG. 9 is a flow chart of a method of operating a drug heating cyclelimiter according to the principles of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is now made in detail to the exemplary embodiments of theinvention, examples of which are illustrated in the accompanyingfigures. Wherever possible, the same reference numbers are usedthroughout the figures to refer to the same or like parts.

FIG. 2 depicts one view of an ophthalmic medical device including adisposable tip segment and a limited reuse assembly according to anembodiment of the present invention. In FIG. 2, the medical deviceincludes a tip segment 205 and a limited reuse assembly 250. The tipsegment 205 includes a needle 210, a housing 215, and an optional light275. The limited reuse assembly 250 includes a housing 255, a switch270, a lock mechanism 265, and a threaded portion 260.

Tip segment 205 is capable of being connected to and removed fromlimited reuse assembly 250. In this embodiment, tip segment 205 has athreaded portion on an interior surface of housing 215 that screws ontothe threaded portion 260 of limited reuse assembly 250. In addition,lock mechanism 265 secures tip segment 215 to limited reuse assembly250. Lock mechanism 265 may be in the form of a button, a slidingswitch, or a cantilevered mechanism. Other mechanisms for connecting tipsegment 205 to limited reuse assembly 250, such as those involvingstructural features that mate with each other, are commonly known in theart and are within the scope of the present invention.

Needle 210 is adapted to deliver a substance, such as a drug, into aneye. Needle 210 may be of any commonly known configuration. Preferably,needle 210 is designed such that its thermal characteristics areconducive to the particular drug delivery application. For example, whena heated drug is to be delivered, needle 210 may be relatively short(several millimeters) in length to facilitate proper delivery of thedrug based on thermal characteristics.

Switch 270 is adapted to provide an input to the system. For example,switch 270 may be used to activate the system or to turn on a heater.Other switches, buttons, or user-directed control inputs are commonlyknown and may be employed with limited reuse assembly 250 and/or tipsegment 205.

Optional light 275 is illuminated when tip segment 205 is ready to beused. Optional light 275 may protrude from housing 215, or it may becontained within housing 215, in which case, optional light 275 may beseen through a clear portion of housing 215. In other embodiments,optional light 275 may be replaced by an indicator, such as a liquidcrystal display, segmented display, or other device that indicates astatus or condition of disposable tip segment 205. For example, optionallight 275 may also pulse on and off to indicate other states, such as,but not limited to a system error, fully charged battery, insufficientlycharged battery or faulty connection between the tip segment 205 andlimited use assembly 250. While shown on tip segment 205, optional light275 or other indicator may be located on limited reuse assembly 250.

FIG. 3 is another embodiment of a limited reuse assembly according tothe principles of the present invention. Limited reuse assembly 250includes a button 310, a display 320, and a housing 330. Disposable tipsegment 205 attaches to end 340 of limited reuse assembly 250. Button310 is actuated to provide an input to the system. As with switch 270,button 310 may activate a heater or other temperature control device orinitiate actuation of a plunger. Display 320 is a liquid crystaldisplay, segmented display, or other device that indicates a status orcondition of disposable tip segment 205 or limited reuse assembly 250.

FIG. 4 is a cross section view of a disposable tip segment and a limitedreuse assembly according to an embodiment of the present invention. FIG.4 shows how tip segment 205 interfaces with limited reuse assembly 250.In the embodiment of FIG. 4, tip segment 205 includes plunger interface420, plunger 415, dispensing chamber housing 425, tip segment housing215, temperature control device 450, thermal sensor 460, needle 210,dispensing chamber 405, interface 530, and tip interface connector 520.Limited reuse assembly 250 includes mechanical linkage 545, actuatorshaft 510, actuator 515, power source 505, controller 305, limited reuseassembly housing 255, interface 535, and limited reuse assemblyinterface connector 525.

In tip segment 205, plunger interface 420 is located on one end ofplunger 415. The other end of plunger 415 forms one end of dispensingchamber 405. Plunger 415 is adapted to slide within dispensing chamber405. An outer surface of plunger 415 is fluidly sealed to the innersurface of dispensing chamber housing 425. Dispensing chamber housing425 surrounds the dispensing chamber 405. Typically, dispensing chamberhousing 425 has a cylindrical shape. As such, dispensing chamber 405also has a cylindrical shape.

Needle 210 is fluidly coupled to dispensing chamber 405. In such a case,a substance contained in dispensing chamber 405 can pass through needle210 and into an eye. Temperature control device 450 at least partiallysurrounds dispensing chamber housing 425. In this case, temperaturecontrol device 450 is adapted to heat and/or cool dispensing chamberhousing 425 and any substance contained in dispensing chamber 405.Interface 530 connects temperature control device 450 and thermal sensor460 with tip interface connector 520.

The components of tip segment 205, including dispensing chamber housing425, temperature control device 450, and plunger 415 are at leastpartially enclosed by tip segment housing 215. In one embodimentconsistent with the principles of the present invention, plunger 415 issealed to the interior surface of dispensing chamber housing 425. Thisseal prevents contamination of any substance contained in dispensingchamber 405. For medical purposes, such a seal is desirable. This sealcan be located at any point on plunger 415 or dispensing chamber housing425.

In limited reuse assembly 250, power source 505 provides power toactuator 515. An interface (not shown) between power source 505 andactuator 515 serves as a conduit for providing power to actuator 515.Actuator 515 is connected to actuator shaft 510. When actuator 515 is astepper motor, actuator shaft 510 is integral with actuator 515.Mechanical linkage interface 545 is connected to actuator shaft 510. Inthis configuration, as actuator 515 moves actuator shaft 510 upwardtoward needle 210 mechanical linkage interface 545 also moves upwardtoward needle 210.

Controller 305 is connected via interface 535 to limited reuse assemblyinterface connecter 525. Limited reuse assembly interface connecter 525is located on a top surface of limited reuse assembly housing 255adjacent to mechanical linkage interface 545. In this manner, bothlimited reuse assembly interface connector 525 and mechanical linkageinterface 545 are adapted to be connected with tip interface connector520 and plunger interface 420 respectively.

Controller 305 and actuator 515 are connected by an interface (notshown). This interface (not shown) allows controller 305 to control theoperation of actuator 515. In addition, an interface (not shown) betweenpower source 505 and controller 305 allows controller 305 to controloperation of power source 505. In such a case, controller 305 maycontrol the charging and the discharging of power source 505 when powersource 505 is a rechargeable battery.

Controller 305 is typically an integrated circuit with power, input, andoutput pins capable of performing logic functions. In variousembodiments, controller 305 is a targeted device controller. In such acase, controller 305 performs specific control functions targeted to aspecific device or component, such as a temperature control device or apower supply. For example, a temperature control device controller hasthe basic functionality to control a temperature control device. Inother embodiments, controller 305 is a microprocessor. In such a case,controller 305 is programmable so that it can function to control morethan one component of the device. In other cases, controller 305 is nota programmable microprocessor, but instead is a special purposecontroller configured to control different components that performdifferent functions. While depicted as one component, controller 305 maybe made of many different components or integrated circuits.

Tip segment 205 is adapted to mate with or attach to limited reuseassembly 250 as previously described. In the embodiment of FIG. 5,plunger interface 420 located on a bottom surface of plunger 415 isadapted to mate with mechanical linkage interface 545 located near a topsurface of limited reuse assembly housing 255. In addition, tipinterface connector 520 is adapted to connect with limited reuseassembly interface connector 525. When tip segment 205 is connected tolimited reuse assembly 250 in this manner, actuator 515 and actuatorshaft 510 are adapted to drive plunger 415 upward toward needle 210. Inaddition, an interface is formed between controller 305 and temperaturecontrol device 450. A signal can pass from controller 305 to temperaturecontrol device 450 through interface 535, limited reuse assemblyinterface connector 525, tip interface connector 520, and interface 530.

In operation, when tip segment 205 is connected to limited reuseassembly 250, controller 305 controls the operation of actuator 515.Actuator 515 is actuated and actuator shaft 510 is moved upward towardneedle 210. In turn, mechanical linkage interface 545, which is matedwith plunger interface 420, moves plunger 415 upward toward needle 210.A substance located in dispensing chamber 405 is then expelled throughneedle 210.

In addition, controller 305 controls the operation of temperaturecontrol device 450. Temperature control device 450 is adapted to heatand/or cool dispensing chamber housing 425. Since dispensing chamberhousing 425 is at least partially thermally conductive, heating orcooling dispensing chamber housing 425 heats or cools a substancelocated in dispensing chamber 405. Temperature information can betransferred from thermal sensor 460 to controller 305 via any of anumber of different interface configurations. This temperatureinformation can be used to control the operation of temperature controldevice 450. When temperature control device 450 is a heater, controller305 controls the amount of current that is sent to temperature controldevice 450. The more current sent to temperature control device 450, thehotter it gets. In such a manner, controller 305 can use a feed backloop utilizing information from thermal sensor 460 to control theoperation of temperature control device 450. Any suitable type ofcontrol algorithm, such as a proportional integral derivative (PID)algorithm, can be used to control the operation of temperature controldevice 450.

FIG. 5 is a cross section view of a disposable tip segment for anophthalmic medical device according to an embodiment of the presentinvention. In FIG. 5, disposable tip segment 205 includes housing 215,needle 210, plunger 415, plunger interface 420, dispensing chamber 405,dispensing chamber housing 425, temperature control device 450, thermalsensor 460, interface 530, and tip interface connector 520. Disposabletip segment 205 operates as a disposable injection device.

In the embodiment of FIG. 5, plunger 415 is located in dispensingchamber housing 425. Dispensing chamber 405 is enclosed by dispensingchamber housing 425 and plunger 415. Plunger 415 forms a fluid seal withthe interior surface of dispensing chamber housing 425. Needle 210 isfluidly coupled to dispensing chamber 405. In this manner, a substancelocated in dispensing chamber 405 can be contacted by plunger 415 andpushed out of needle 210. Temperature control device 450 is locatedadjacent to dispensing chamber housing 425 and at least partiallysurrounds dispensing chamber 405. Housing 215 forms an outer skin ondisposable tip segment 205.

In various embodiments of the present invention, temperature controldevice 450 is a heating and/or a cooling device. Temperature controldevice 450 is in thermal contact with dispensing chamber housing 425. Assuch, temperature control device 450 is capable of changing thetemperature of the substance in dispensing chamber 405. Interface 530and tip interface connector 520 couple temperature control device 450 toa limited reuse assembly. In such a case, temperature control device 450can be powered and controlled by the limited reuse assembly. In oneembodiment of the present invention, temperature control device 450receives voltage via interface 530 from a limited reuse assembly.Providing a positive voltage across the temperature control device 450causes it to produce heat. Providing a negative voltage across thetemperature control device 450 causes it to cool.

A substance to be delivered into an eye, typically a drug, is located indispensing chamber 405. In this manner, the substance is contacted bythe inner surface of dispensing chamber housing 425 and one face ofplunger 415. Typically, dispensing chamber 405 is cylindrical in shape.Temperature control device 450 is in thermal contact with dispensingchamber housing 425. In this manner, temperature control device 450 isadapted to control the temperature of the contents of dispensing chamber425. Thermal sensor 460 provides temperature information to assist incontrolling the operation of temperature control device 450.

In one embodiment of the present invention, the substance located indispensing chamber 405 is a drug that is preloaded into the dispensingchamber. In such a case, disposable tip segment 205 is appropriate as asingle use consumable product. Such a disposable product can beassembled at a factory with a dosage of a drug installed.

When a drug is preloaded into dispensing chamber 405, a set quantity ofthe drug can be preloaded. For example, 100 microliters of a drug can beloaded into dispensing chamber 405, and any quantity up to 100microliters can be dispensed. In such a case, the plunger 415 can bemoved a precise distance to deliver a precise dosage of drug from thedispensing chamber 405, through the needle 210, and into an eye. Thisprovides for flexibility of dosing and for ease of assembly.

FIG. 6 is a block diagram of an implementation of a drug heating cyclelimiter according to the principles of the present invention. In FIG. 6,controller 305 interfaces with temperature control device 450 andthermal sensor 460. Controller 305 receives temperature information fromthermal sensor 460 and uses that information to control temperaturecontrol device 450.

FIG. 7 is a block diagram of an implementation of a drug heating cyclelimiter according to the principles of the present invention. In FIG. 7,controller 305 includes counter 720 and timer 730. Controller 305interfaces with thermal sensor 460 and switch 710. Switch 710 interfaceswith temperature control device 450. In the embodiment of FIG. 7,controller 305 controls the operation of switch 710 to supply a firstvoltage (V1) or a second voltage (V2) to temperature control device 450.

Switch 710 is any suitable type of mechanical or electronic switch.Since the voltage supplied to temperature control device 450 istypically a low DC voltage, any number of different electronicallyimplemented switches may be used. In one embodiment, a comparator isused as switch 710. Controller 305 provides an input to control switch710.

Controller 305 also includes a counter 720 and a timer 730. While shownas separate blocks within controller 305, counter 720 and timer 730 maybe implemented with software or hardware contained in controller 305.Many electronic controllers, such as microcontrollers, contain suchtiming and counting functions. Counter 720 provides a counting function,and timer 730 provides a timing function.

In operation, controller 305 operates switch 710 to provide a firstvoltage (V1) to temperature control device 450. This first voltage (V1)is typically higher then the second voltage (V2). The first voltage (V1)brings the temperature control device to a set point temperaturequickly. When temperature control device 450 is a heater, such as aresistive heater, applying a relatively high first voltage (V1) bringsthe temperature of the heater up quickly. Thermal sensor 460 measuresthe temperature of the heater (or a temperature near the heater) andprovides this information to controller 305. When this temperaturereaches the set point, controller 305 operates switch 710 to provide thesecond voltage (V2) to temperature control device 450. Again, whentemperature control device 450 is a heater, this second, relativelylower voltage (V2), maintains temperature control device 450 at the setpoint. In sum, the first voltage (V1) is chosen to bring the temperaturecontrol device 450 to a desired temperature quickly, and the secondvoltage (V2) is chosen to maintain the temperature control device 450 atthe desired temperature.

Counter 720 counts the number of times the temperature control device450 is operated to alter the temperature of a substance contained in thedispensing chamber. Since the substance in the dispensing chamber istypically a drug, it is desirable not to stress the drug with excessheat or elevated temperatures. For example, when a drug is suspended ina phase transition compound, the phase transition compound is heated tobring it to a more liquid state suitable for injection into the eye. Toomuch heat may have a negative effect on the drug or may degrade it.Therefore, it can be important to monitor the amount of heat that isapplied to the drug. Counter 720 achieves this by counting the number ofheating cycles the drug undergoes. For example, if a doctor turns on thetemperature control device to heat the phase transition compound, andthen leaves the device on without performing an injection, the deviceturns itself off after a preset period of time (the time the device isleft on is calculated by timer 730). The doctor may then turn the deviceon a second time, in which case the counter increments by one. After apreset number of counts are reached, the device is disabled indicatingthat the drug has been exposed to a level of heating that is notdesirable. In such a case, the tip segment may be disabled to prevent itfrom being used.

Timer 730 tracks the amount of time that temperature control device 450is on (and altering the temperature of the drug/phase transitioncompound). Timer 730 begins timing when the temperature control device450 is turned on or when it reaches a steady state temperature. In thismanner, timer 730 keeps track of how long the drug is exposed to heat(when temperature control device 450 is a heater). In conjunction withcounter 720, timer 730 can be used to determine how much heat is appliedto the drug.

FIG. 8 is a graph of one operation of a drug heating cycle limiteraccording to the principles of the present invention. In FIG. 8, time isdepicted on the x-axis and temperature on the y-axis. At time, t, thevoltage applied across temperature control device 450 is switched fromV1 to V2. The temperature of temperature control device 450 (when it isa heater) is depicted. The temperature, T, is the set point or steadystate temperature. In this manner, voltage V1 is applied to bringtemperature control device to its set point in a relatively quickmanner, and voltage V2 is applied to maintain temperature control deviceat the set point.

FIG. 9 is a flow chart of a method of operating a drug heating cyclelimiter according to the principles of the present invention. In 1110,it is determined whether the limit number has been reached. The limitnumber is the preset number of times that the temperature control deviceis allowed to cycle in the tip segment. Each cycle corresponds to aheating of the drug in the dispensing chamber. For example, this limitnumber may be five. In such a case, the temperature control device in atip segment is allowed to cycle five times before being disabled. If in1110, the limit number has been reached, then the system is disabled in1130. In one embodiment, a fuse located in the tip segment is blown toprevent its reuse. If the limit number has not been reached, then in1120, the counter is incremented. Incrementing the counter indicatesthat the temperature control device is to be cycled.

In 1140, a first voltage V1 is applied to the temperature controldevice. In 1150, it is determined whether the temperature control devicehas reached the steady state temperature (or set point). If it has notreached its steady state temperature, then the first voltage V1continues to be applied across the temperature control device. If it hasreached its steady state temperature, then in 1160, the second voltageV2 is applied to the temperature control device. As previouslymentioned, this second voltage V2 keeps the temperature control deviceat the steady state temperature. In 1170, the timer is started. Thistimer counts the amount of time that the temperature control device isat the steady state temperature (and heating the drug—when thetemperature control device is a heater).

In 1180, it is determined whether the time limit has been reached. Thetime limit is the amount of time that the temperature control device isallowed to be left on without an injection being performed. In oneembodiment, the time limit is five minutes. In such a case, thetemperature control device is allowed to be on for five minutes. If thedoctor does not perform the injection procedure within five minutes,then the time limit has been reached. In such a case, the system isturned off (1190).

From the above, it may be appreciated that the present inventionprovides an improved system for delivering precise volumes of asubstance into an eye. The present invention provides a single use,disposable delivery device tip segment that is capable of delivering adosage of a drug. The tip segment interfaces with a limited reuseassembly. The disposable tip segment has a temperature control deviceand a thermal sensor. The system monitors the amount of time that thetemperature control device is turned on and the number of cycles thatthe temperature control device undergoes. Preset limits on thesevariables are used to prevent further use of the device when the limitsare exceeded. In this manner, the drug contained in the tip segment isnot subjected to excessive temperature stresses.

While the present invention is described in the context of a single-useophthalmic drug delivery device, the present invention encompasses anymedical device or injection device. Other embodiments of the inventionwill be apparent to those skilled in the art from consideration of thespecification and practice of the invention disclosed herein. It isintended that the specification and examples be considered as exemplaryonly, with a true scope and spirit of the invention being indicated bythe following claims.

1. A dispensing assembly comprising: a dispensing chamber housing havingan inner surface and an outer surface, the inner surface partiallydefining a dispensing chamber for receiving a quantity of a substance; atemperature control device at least partially surrounding the dispensingchamber housing, the temperature control device for altering atemperature of a substance in the dispensing chamber; a thermal sensorlocated near the temperature control device, the thermal sensor forreading a temperature near the temperature control device; and acontroller for controlling the temperature control device such that thesubstance in the dispensing chamber is not exposed to elevatedtemperature nor overexposed to heat.
 2. The assembly of claim 1 whereinthe controller counts a number of times the temperature control deviceis activated.
 3. The assembly of claim 2 wherein the controller disablesa tip segment if the number of times the temperature control device isactivated exceeds a set number.
 4. The assembly of claim 1 wherein thecontroller times a period when the temperature control device isactivated.
 5. The assembly of claim 4 wherein the controller shuts offthe temperature control device when the period when the temperaturecontrol device is activated exceeds a set period.
 6. The assembly ofclaim 1 further comprising: a switch coupled to the temperature controldevice.
 7. The assembly of claim 6 wherein the controller controls theswitch such that a first voltage is applied to the temperature controldevice until the temperature control device reaches a desiredtemperature, and a second voltage is applied to the temperature controldevice thereafter to maintain the temperature control device at thedesired temperature.
 8. The assembly of claim 1 wherein the temperaturecontrol device is a heater comprising a resistive element.
 9. Aninjection assembly comprising: a dispensing chamber housing having aninner surface and an outer surface, the inner surface partially defininga dispensing chamber for receiving a quantity of a substance; atemperature control device at least partially surrounding the dispensingchamber housing, the temperature control device for altering atemperature of a substance in the dispensing chamber; a thermal sensorlocated near the temperature control device, the thermal sensor forreading a temperature near the temperature control device; a switchcoupled to the temperature control device; and a controller forcontrolling the temperature control device; wherein the controllercontrols the switch such that a first voltage is applied to thetemperature control device until the temperature control device reachesa desired temperature, and a second voltage is applied to thetemperature control device thereafter to maintain the temperaturecontrol device at the desired temperature.
 10. The assembly of claim 9wherein the controller counts a number of times the temperature controldevice is activated.
 11. The assembly of claim 10 wherein the controllerdisables a tip segment if the number of times the temperature controldevice is activated exceeds a set number.
 12. The assembly of claim 9wherein the controller times a period when the temperature controldevice is activated.
 13. The assembly of claim 12 wherein the controllershuts off the temperature control device when the period when thetemperature control device is activated exceeds a set period.
 14. Theassembly of claim 9 wherein the temperature control device is a heatercomprising a resistive element.
 15. A method of operating a dispensingassembly comprising: checking a count of a number of times a temperaturecontrol device has been activated; if the count does not exceed a presetnumber, incrementing a counter; applying a first voltage across atemperature control device to bring the temperature control device to adesired temperature; after the temperature control device reaches thedesired temperature, applying a second voltage across the temperaturecontrol device to maintain the temperature control device at the desiredtemperature; starting a timer to count the amount of time that thetemperature control device is activated; and if the amount of time thatthe temperature control device is activated exceeds a preset amount oftime, turning off the temperature control device.
 16. The method ofclaim 15 further comprising: if the count exceeds a preset number, thendisabling a tip segment so that an injection cannot be performed. 17.The method of claim 15 wherein applying a first voltage across atemperature control device to bring the temperature control device to adesired temperature further comprises controlling a switch to apply thefirst voltage.
 18. The method of claim 17 wherein applying a secondvoltage across a temperature control device to bring the temperaturecontrol device to a desired temperature further comprises controlling aswitch to apply the second voltage.
 19. The method of claim 18 whereinstarting a timer to count the amount of time that the temperaturecontrol device is activated further comprises starting the timer whenthe switch is controlled to apply the second voltage.
 20. The method ofclaim 15 wherein starting a timer to count the amount of time that thetemperature control device is activated further comprises starting thetimer after the temperature control device has reached the desiredtemperature.